Assume, we have model
class BaseModel(models.Model):
is_a = models.BooleanField()
and two models related to this one:
class A(models.Model):
value_1 = models.IntegerField()
base = models.ForeignKey(BaseModel, related_name='a')
class B(models.Model):
value_1 = models.IntegerField()
value_2 = models.IntegerField()
base = models.ForeignKey(BaseModel, related_name='b')
What I need is to refer to A or B depending on is_a property.
For example,
base = BaseModel.objects.get(id=1)
if base.is_a:
obj = A.objects.create(value_1=1, base=base)
else:
obj = B.objects.create(value_1=1, value_2=2, base=base)
return obj
or
if base.is_a:
queryset = base.a.all()
else:
queryset = base.b.all()
return queryset
i.e., every time I have to check the is_a property.
Is there more graceful way?
There are two only related models, A and B, no other ones will appear in the nearest future.
Part of the problem can be solved with django-polymorphic, e.g.:
class A(PolymorphicModel):
...
class B(A):
...
This allows to retrieve all A's and B's with one request like base.b.all(), but the problem here is that every B creates instance of A, which is unwanted.
I've considered GenericForeignKey as well. As far as I understood it has a number of limitations like "1) You can't use GenericForeignKey in query filters ; 2) a GenericForeignKey won't appear in a ModelForm" (from GenericForeignKey or ForeignKey).
One idea is to add choices to the BaseModel to have a string representation of your boolean value. If you set the strings equal to the A and B model names, you can use the model.get_foo_display() method to return the name of the model. Then use the Python getattr() method to access attributes as variables.
class BaseModel(models.Model):
base_model_choices = (
(True, 'A'),
(False, 'B'),
)
is_a = models.BooleanField(choices=base_model_choices)
For example,
base = BaseModel.objects.get(id=1)
queryset = base.getattr(models, get_is_a_display()).all()
obj = getattr(models, get_is_a_display()).objects.create(base=base)